Congenital Anomalies of the Heart 17 



any description of the heart which revealed an understanding or 

 recognition of this portion of the septum. 



Huschka (1855) described the thin area on the basis of a study 

 of 300 hearts ; he pointed out that it was always present and was 

 a normal structure. He corrected Schliemann's error and claimed 

 that he was the first to discover and describe the structure as 

 a normal part of the heart. Peacock (1855) described its pres- 

 ence normally, designated it as " the undefended space " and so 

 liable to developmental error. He seemed to think at this time 

 that this point was the most frequent seat of septal defect, an 

 error corrected somewhat later. Reinhard (1857) suggested the 

 name " pars membranacea," which has been quite generally ac- 

 cepted. 



Rokitansky (1875) studied the development of the septum and 

 on this basis divided the base into a posterior muscular portion, a 

 pars membranacea, and an anterior fleshy portion, the latter being 

 subdivided into an anterior and posterior portion. Defects occur 

 most frequently in the posterior part of the anterior septum 

 (Rokitansky) and less frequently in the pars membranacea 

 When the defect is in the anterior part of the anterior septum 

 Keith has shown that it is an anomaly of the bulbar septum. De- 

 fects of the septum near the apex are extremely rare and may 

 be multiple. 



Septum defect is frequently encountered in conjunction with 

 stenosis of the pulmonary artery and the question as to which 

 is the primary lesion has been much discussed. Hunter (1786) 

 was the first, I believe, to suggest that the obstruction of the 

 pulmonary circulation prevented the closure of the septum. 

 Other theories have been so frequently discussed that they do 

 not need review here. It must be noted in examining any theory 

 that many examples have been found of each lesion occurring 

 without the other. As I interpret the later experimental work 

 in teratology it reveals a much less interdependence of parts in 

 development than was formerly supposed and suggests a much 

 more obscure disturbing factor than simple mechanics. 



The total number of septal anomalies is 594; of these 99 or 

 16.6 per cent, are total absence of septum, listed as follows : 



